This disclosure relates generally to the reduction of defects in the appearance surfaces of a powder coated substrate.
Coating powders are dry, finely divided, free flowing, solid materials at room temperature. Upon application to a surface, they are heated to fuse and optionally cure, thereby forming an even, uniform coating. In many surface-finishing applications, only the appearance surface of substrate is coated. During the curing cycle moisture is driven from the core of the substrate to the outer surfaces thereof, where it evaporates, ultimately causing the substrate to shrink. Where the substrate is fabricated from a hygroscopic material, over time moisture is absorbed through the non-coated non-appearance surface, ultimately causing the substrate to expand. Upon expansion of the substrate, the substrate may become warped and the coating may be stressed, oftentimes to the point at which interruptions occur in the continuity of the coating, thereby resulting in the formation of blemishes, cracks, or other surface defects.
One approach to reducing defects in a powder coated appearance surface having edges, corners, profiles, or other discontinuities involves the machining of grooves, channels, or holes into the non-coated non-appearance surface of the substrate (the surface opposing the appearance surface). The machining of such grooves, channels, or holes facilitates the out-gassing of volatiles from the substrate through the non-appearance surface by providing sufficient pathways for the volatile components to escape. While allowing the escape of volatiles through the non-appearance surface oftentimes reduces cracking of a coating applied to the appearance surface, the absorption of moisture through the nonappearance surface may be sufficient to cause the substrate material to expand and warp, which may subsequently lead to the stressing of the coating.
Accordingly, there exists a need for methods to reduce surface defects in the powder coating, particularly for surfaces where the absorption of moisture causes the substrate to expand and stress the coating.
In one aspect, a method of reducing the formation of surface defects in a coated substrate includes providing coating powders at both the appearance surfaces and the non-appearance surfaces of the substrate.
In another aspect, a method of coating the substrate includes disposing a first powder at the appearance surface of the substrate, and disposing a second powder at the non-appearance surface of the substrate. A method of facilitating the adherence of a coating at an edge between two surfaces of the substrate includes configuring the edge to have a rounded surface.